Clean up a number of 2.19 opt outs in language tests.

This is less than half of them, will send some other chunks later.

Bug:51557
Change-Id: I4e80812a689fde99e23c34b6405aaf57cd431ce8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/289261
Reviewed-by: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Jake Macdonald <jakemac@google.com>

tests/corelib/map_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 library map_test;
 
 import "package:expect/expect.dart";
@@ -858,7 +854,7 @@ class Mutable {
 }
 
 // Slow implementation of Map based on MapBase.
-abstract class MapBaseOperations<K, V> {
+mixin class MapBaseOperations<K, V> {
   final List _keys = <K>[];
   final List _values = <V>[];
   int _modCount = 0;

tests/corelib/map_update_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 import 'dart:collection';
 import 'dart:convert' show json;
@@ -130,7 +126,7 @@ void testNonNull(Map<Comparable?, Object?> map) {
 }
 
 // Slow implementation of Map based on MapBase.
-abstract class MapBaseOperations<K, V> {
+mixin class MapBaseOperations<K, V> {
   final List _keys = <K>[];
   final List _values = <V>[];
   int _modCount = 0;

tests/language/abstract/getter2_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 class A {
@@ -25,7 +21,7 @@ class C extends B {
   int get x => super.x;
 }
 
-class GetterConcrete {
+mixin class GetterConcrete {
   var _foo;
 
   get foo => _foo;

tests/language/call/method_as_cast_test.dart

@@ -2,8 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/call/method_implicit_invoke_instance_test.dart

@@ -2,8 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/call/method_implicit_invoke_local_runtime_1_test.dart

@@ -5,8 +5,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/call/method_implicit_invoke_local_runtime_2_test.dart

@@ -5,8 +5,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/call/method_implicit_invoke_local_runtime_3_test.dart

@@ -5,8 +5,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/call/method_implicit_invoke_local_runtime_4_test.dart

@@ -5,8 +5,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/call/method_implicit_invoke_local_runtime_test.dart

@@ -5,8 +5,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/call/method_implicit_invoke_local_test.dart

@@ -2,8 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/call/method_implicit_invoke_static_test.dart

@@ -2,8 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/call/method_implicit_invoke_top_level_test.dart

@@ -2,8 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/call/method_is_check_test.dart

@@ -2,8 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Implements Function which is not allowed in Dart 3.
 // @dart=2.19
 
 // Dart test program to test arithmetic operations.

tests/language/class/override_inference_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that inheriting types on overriding members work as specified.
 
 // ignore_for_file: unused_local_variable
@@ -47,7 +43,7 @@ class INumInt {
   int foo(num x) => x.toInt();
 }
 
-class IIntNum {
+mixin class IIntNum {
   num foo(int x) => x.toInt();
 }
 

tests/language/const/constructor_mixin2_test.dart

@@ -2,11 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
-class Mixin {
+mixin Mixin {
   var nonFinalField;
 }
 

tests/language/const/constructor_mixin3_test.dart

@@ -2,11 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
-class Mixin {}
+mixin Mixin {}
 
 class A {
   const A();

tests/language/const/constructor_mixin_test.dart

@@ -2,11 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
-class Mixin {}
+mixin Mixin {}
 
 class A {
   const A(foo);

tests/language/constructor/missing_initializer_test.dart

@@ -2,17 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that it is an error for a class with no generative constructors to
 // have a final instance variable without an initializing expression, except
 // if it is `abstract` or `external`. The latter also holds in a class with
 // generative constructors.
 
 // Has factory, hence no default, hence no generative constructors.
-abstract class A {
+abstract mixin class A {
   final dynamic n;
   //            ^
   // [analyzer] COMPILE_TIME_ERROR.FINAL_NOT_INITIALIZED

tests/language/constructor/with_mixin_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test super constructor invocation with mixins.
 // Regression test for issue dartbug.com/22604
 
@@ -21,7 +17,7 @@ class A {
   }
 }
 
-class I {}
+mixin I {}
 
 class B extends A with I {
   int y;

tests/language/covariant/setter_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 class A {}
@@ -67,11 +63,11 @@ abstract class D<T> {
   void set m1(T x);
 }
 
-class E {
+mixin E {
   void set m1(A x) {}
 }
 
-class F = Object with E implements D<A>;
+mixin class F = Object with E implements D<A>;
 class G = C with E implements D<A>;
 
 class H extends Object with E implements D<A> {}

tests/language/covariant/subtyping_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import 'package:expect/expect.dart';
 
 class Fields<T> {
@@ -132,7 +128,7 @@ testFieldOfGenericFunctionType() {
   cNum.g(42);
 }
 
-class Base {
+mixin class Base {
   int _t = 0;
   add(int t) {
     _t += t;

tests/language/covariant/subtyping_with_mixin_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import 'package:expect/expect.dart';
 
 class A {}
@@ -14,7 +10,7 @@ class B extends A {}
 
 class Base<S> {}
 
-class Mixin<T> {
+mixin Mixin<T> {
   void f(T arg) {}
 }
 

tests/language/covariant_override/tear_off_type_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 // If a parameter is directly or indirectly a covariant override, its type in
@@ -21,11 +17,11 @@ typedef void TakeOptionalObjectsAndInts([Object? a, int b, Object? c, int d]);
 typedef void TakeNamedInts({int a, int b, int c, int d});
 typedef void TakeNamedObjectsAndInts({Object? a, int b, Object? c, int d});
 
-class M1 {
+mixin M1 {
   method(covariant int a, int b) {}
 }
 
-class M2 {
+mixin M2 {
   method(int a, covariant int b) {}
 }
 
@@ -87,11 +83,11 @@ class Interface2 {
   void method(int a, covariant int b, int c, int d, int e) {}
 }
 
-class Mixin1 {
+mixin Mixin1 {
   void method(int a, int b, covariant int c, int d, int e) {}
 }
 
-class Mixin2 {
+mixin Mixin2 {
   void method(int a, int b, int c, covariant int d, int e) {}
 }
 

tests/language/deferred/inheritance_constraints_runtime_test.dart

@@ -5,14 +5,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 import "inheritance_constraints_lib.dart" deferred as lib;
 
-class Foo {}
+mixin class Foo {}
 
 class Foo2 extends D {}
 

tests/language/deferred/mixin_lib1.dart

@@ -2,16 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 library lib1;
 
 import "mixin_shared.dart";
 import "mixin_test.dart";
 
-class Mixin {
+mixin class Mixin {
   foo() => "lib1.Mixin";
 }
 

tests/language/deferred/mixin_shared.dart

@@ -2,12 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 library shared;
 
-class SharedMixin {
+mixin SharedMixin {
   foo() => "SharedMixin";
 }

tests/language/deferred/mixin_test.dart

@@ -2,25 +2,21 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 
 import "mixin_lib1.dart" deferred as lib1;
 import "mixin_lib2.dart" deferred as lib2;
 
-class NonDeferredMixin {
+mixin class NonDeferredMixin {
   foo() => "NonDeferredMixin";
 }
 
-class NonDeferredMixin1 {
+mixin class NonDeferredMixin1 {
   foo() => "NonDeferredMixin1";
 }
 
-class NonDeferredMixin2 {
+mixin class NonDeferredMixin2 {
   foo() => "NonDeferredMixin2";
 }
 

tests/language/generic/constructor_mixin2_runtime_test.dart

@@ -5,10 +5,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
@@ -18,9 +14,9 @@ class A<X> {
   A(X x);
 }
 
-class B {}
+mixin B {}
 
-class C {}
+mixin C {}
 
 class D<Y> = A<Y> with B, C;
 

tests/language/generic/constructor_mixin2_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
@@ -15,9 +11,9 @@ class A<X> {
   A(X x);
 }
 
-class B {}
+mixin B {}
 
-class C {}
+mixin C {}
 
 class D<Y> = A<Y> with B, C;
 

tests/language/generic/constructor_mixin3_runtime_test.dart

@@ -5,10 +5,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
@@ -18,7 +14,7 @@ class A<X> {
   A(X x);
 }
 
-class B {}
+mixin B {}
 
 class C1 = A<int> with B;
 class C2 = A<String> with B;

tests/language/generic/constructor_mixin3_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
@@ -15,7 +11,7 @@ class A<X> {
   A(X x);
 }
 
-class B {}
+mixin B {}
 
 class C1 = A<int> with B;
 class C2 = A<String> with B;

tests/language/generic/constructor_mixin_runtime_test.dart

@@ -5,10 +5,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
@@ -18,7 +14,7 @@ class A<X> {
   A(X x);
 }
 
-class B {}
+mixin B {}
 
 class C<Y> = A<Y> with B;
 

tests/language/generic/constructor_mixin_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
@@ -15,7 +11,7 @@ class A<X> {
   A(X x);
 }
 
-class B {}
+mixin B {}
 
 class C<Y> = A<Y> with B;
 

tests/language/generic/field_mixin2_test.dart

@@ -2,15 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
 
-class M<T> {
+mixin M<T> {
   var field = T;
 }
 

tests/language/generic/field_mixin3_test.dart

@@ -2,15 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
 
-class M<T> {
+mixin M<T> {
   var field = new A<int>() is A<T>;
 }
 

tests/language/generic/field_mixin4_test.dart

@@ -2,15 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
 
-class M<T> {
+mixin M<T> {
   bool field = () {
     try {
       throw 0;

tests/language/generic/field_mixin5_test.dart

@@ -2,15 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
 
-class M<T> {
+mixin M<T> {
   Type field = () {
     return T;
   }();

tests/language/generic/field_mixin6_runtime_test.dart

@@ -5,15 +5,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
 
-class M<T> {
+mixin M<T> {
 
   T field2 = 0 as dynamic;
 }

tests/language/generic/field_mixin6_test.dart

@@ -2,15 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
 
-class M<T> {
+mixin M<T> {
   T field1 = 0;
   //         ^
   // [analyzer] COMPILE_TIME_ERROR.INVALID_ASSIGNMENT

tests/language/generic/field_mixin_test.dart

@@ -2,15 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
 
-class M<T> {
+mixin M<T> {
   var field = new A<T>();
 }
 

tests/language/generic/instanceof5_test.dart

@@ -2,17 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test that instanceof works correctly with type variables.
 
 import "package:expect/expect.dart";
 
 class A {}
 
-class B<T, S> {}
+mixin B<T, S> {}
 
 class C<U, V> extends A with B<V, U> {}
 

tests/language/generic/method_types_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import 'package:expect/expect.dart';
 
 typedef Convert1<O> = O Function<I>(I input);
@@ -13,7 +9,7 @@ typedef Convert2<I> = O Function<O>(I input);
 typedef Convert3 = O Function<I, O>(I input);
 typedef Other(a, b);
 
-class Mixin<E> {
+mixin Mixin<E> {
   E convert1<I>(I input) => throw "uncalled";
 }
 

tests/language/malformed/inheritance_test.dart

@@ -2,14 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Tests that malformed types used in extends, implements, and with clauses
 // cause compile-time errors.
 
-class A<T> {}
+mixin class A<T> {}
 
 class C
     extends Unresolved

tests/language/mixin/abstract_getter_test.dart

@@ -2,13 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import 'package:expect/expect.dart';
 
-abstract class B {
+mixin B {
   int get x;
 }
 

tests/language/mixin/accessor_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Regression test case for DDC bug where if a getter/setter is mixed in
 // without a corresponding getter/setter, DDC fails to install a the
 // corresponding getter/setter that calls super.
@@ -19,7 +15,7 @@ abstract class C<E> {
   operator []=(int index, E value);
 }
 
-abstract class CMixin<E> implements C<E> {
+mixin CMixin<E> implements C<E> {
   E get first => this[0];
   set first(E x) {
     this[0] = x;
@@ -28,7 +24,7 @@ abstract class CMixin<E> implements C<E> {
 
 abstract class CBase<E> extends Object with CMixin<E> {}
 
-abstract class DMixin<E> implements C<E> {
+mixin DMixin<E> implements C<E> {
   set first(E _) => throw new UnsupportedError('');
   operator []=(int index, E value) => throw new UnsupportedError('');
 }
@@ -41,7 +37,7 @@ class DView<E> extends DBase<E> {
   E operator [](int index) => _source.elementAt(index);
 }
 
-abstract class FMixin<E> implements C<E> {
+mixin FMixin<E> implements C<E> {
   E get first => throw new UnsupportedError('');
   E operator [](int index) => throw new UnsupportedError('');
 }

tests/language/mixin/and_extension_member_test.dart

@@ -2,14 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import 'dart:collection';
 import 'package:expect/expect.dart';
 
-class OverrideFirstGetter {
+mixin OverrideFirstGetter {
   get first => 9999;
 }
 

tests/language/mixin/black_listed_test.dart

@@ -2,17 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Check mixin of black-listed types.
 
 import 'package:expect/expect.dart';
 
-class C {}
+mixin C {}
 
-class D {}
+mixin D {}
 
 class C1 extends Object
 with String //# 01: compile-time error

tests/language/mixin/bound_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 // library abstract_expressions;
@@ -29,23 +25,23 @@ abstract class AbstractNumber {
 
 // library evaluator;
 
-abstract class ExpressionWithEval {
+abstract mixin class ExpressionWithEval {
   int get eval;
 }
 
-abstract class AdditionWithEval<E extends ExpressionWithEval> {
+abstract mixin class AdditionWithEval<E extends ExpressionWithEval> {
   E get operand1;
   E get operand2;
   int get eval => operand1.eval + operand2.eval;
 }
 
-abstract class SubtractionWithEval<E extends ExpressionWithEval> {
+abstract mixin class SubtractionWithEval<E extends ExpressionWithEval> {
   E get operand1;
   E get operand2;
   int get eval => operand1.eval - operand2.eval;
 }
 
-abstract class NumberWithEval {
+abstract mixin class NumberWithEval {
   int get val;
   int get eval => val;
 }
@@ -61,7 +57,7 @@ abstract class AbstractMultiplication<E> {
 
 // import 'evaluator.dart' show ExpressionWithEval;
 
-abstract class MultiplicationWithEval<E extends ExpressionWithEval> {
+abstract mixin class MultiplicationWithEval<E extends ExpressionWithEval> {
   E get operand1;
   E get operand2;
   int get eval => operand1.eval * operand2.eval;
@@ -69,30 +65,30 @@ abstract class MultiplicationWithEval<E extends ExpressionWithEval> {
 
 // library string_converter;
 
-abstract class ExpressionWithStringConversion {
+abstract mixin class ExpressionWithStringConversion {
   String toString();
 }
 
-abstract class AdditionWithStringConversion<
+abstract mixin class AdditionWithStringConversion<
     E extends ExpressionWithStringConversion> {
   E get operand1;
   E get operand2;
   String toString() => '($operand1 + $operand2))';
 }
 
-abstract class SubtractionWithStringConversion<
+abstract mixin class SubtractionWithStringConversion<
     E extends ExpressionWithStringConversion> {
   E get operand1;
   E get operand2;
   String toString() => '($operand1 - $operand2)';
 }
 
-abstract class NumberWithStringConversion {
+abstract mixin class NumberWithStringConversion {
   int get val;
   String toString() => val.toString();
 }
 
-abstract class MultiplicationWithStringConversion<
+abstract mixin class MultiplicationWithStringConversion<
     E extends ExpressionWithStringConversion> {
   E get operand1;
   E get operand2;

tests/language/mixin/cyclic_runtime_test.dart

@@ -5,17 +5,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test for cyclicity check on named mixin applications.
 
 class A<T> {}
 
 class S {}
 
-class M<T> {}
+mixin M<T> {}
 
 class C1 = S with M;
 

tests/language/mixin/cyclic_test.dart

@@ -2,17 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test for cyclicity check on named mixin applications.
 
 class A<T> {}
 
 class S {}
 
-class M<T> {}
+mixin M<T> {}
 
 class C1 = S with M;
 class C2 = S with C2;

tests/language/mixin/extends_field_test.dart

@@ -2,21 +2,17 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 class S {
   var foo = "S-foo";
 }
 
-class M1 {
+mixin M1 {
   final bar = "M1-bar";
 }
 
-class M2 {
+mixin M2 {
   var baz = "M2-baz";
 }
 

tests/language/mixin/extends_is_test.dart

@@ -2,17 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 class S {}
 
-class M1 {}
+mixin M1 {}
 
-class M2 {}
+mixin M2 {}
 
 class C extends S with M1 {}
 

tests/language/mixin/extends_method_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 class S {
@@ -13,12 +9,12 @@ class S {
   baz() => "S-baz";
 }
 
-class M1 {
+mixin M1 {
   static m1bar() => "M1-bar";
   bar() => m1bar();
 }
 
-class M2 {
+mixin M2 {
   bar() => "M2-bar";
   baz() => "M2-baz";
   fez() => "M2-fez";

tests/language/mixin/factory_constructor_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 class Base {
@@ -15,7 +11,7 @@ class Base {
   }
 }
 
-abstract class Mixin implements Base {
+abstract mixin class Mixin implements Base {
   final x = "hello";
   factory Mixin() => new _MixinAndBase._();
 }

tests/language/mixin/field_initializer_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Dart test program for testing throw statement
 
 import 'package:expect/expect.dart';
@@ -17,7 +13,7 @@ class S {
 
 good_stuff() => "Glenfiddich";
 
-class M {
+mixin class M {
   var m1 = good_stuff();
   static good_stuff() => "Macallen";
 }

tests/language/mixin/field_test.dart

@@ -2,21 +2,17 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 class S {
   var foo = "S-foo";
 }
 
-class M1 {
+mixin M1 {
   final bar = "M1-bar";
 }
 
-class M2 {
+mixin M2 {
   var baz = "M2-baz";
 }
 

tests/language/mixin/forwarding_constructor1_test.dart

@@ -2,17 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
-abstract class Mixin1 {
+mixin Mixin1 {
   var mixin1Field = 1;
 }
 
-abstract class Mixin2 {
+mixin Mixin2 {
   var mixin2Field = 2;
 }
 

tests/language/mixin/forwarding_constructor2_test.dart

@@ -2,17 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
-abstract class Mixin1 {
+mixin Mixin1 {
   var mixin1Field = 1;
 }
 
-abstract class Mixin2 {
+mixin Mixin2 {
   var mixin2Field = 2;
 }
 

tests/language/mixin/forwarding_constructor3_test.dart

@@ -2,20 +2,16 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Verify that a named mixin constructor forwards to the corresponding named
 // base class constructor.
 
 import "package:expect/expect.dart";
 
-abstract class Mixin1 {
+mixin Mixin1 {
   var mixin1Field = 1;
 }
 
-abstract class Mixin2 {
+mixin Mixin2 {
   var mixin2Field = 2;
 }
 

tests/language/mixin/forwarding_constructor4_test.dart

@@ -2,14 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Verify that a forwarding constructor is generated even when there is an
 // optional parameter.
 
-abstract class Mixin {}
+mixin Mixin {}
 
 class Base {
   Base(

tests/language/mixin/forwarding_stub_call_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test for calling a method for which a forwarding super stub has been
 // inserted.
 
@@ -15,7 +11,7 @@ class Super<T> {
   void method(T t) {}
 }
 
-class Mixin {
+mixin Mixin {
   void method(int t) {}
 }
 

tests/language/mixin/forwarding_stub_set_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test for assigning to a field for which a forwarding super stub has been
 // inserted.
 
@@ -15,7 +11,7 @@ class Super<T> {
   T? field;
 }
 
-class Mixin {
+mixin Mixin {
   int? field;
 }
 

tests/language/mixin/forwarding_stub_tearoff_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Test for tearing off a method for which a forwarding super stub has been
 // inserted.
 
@@ -15,7 +11,7 @@ class Super<T> {
   void method(T t) {}
 }
 
-class Mixin {
+mixin Mixin {
   void method(int t) {}
 }
 

tests/language/mixin/generic_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 class S<T> {
@@ -14,13 +10,13 @@ class S<T> {
   }
 }
 
-class M<T> {
+mixin M<T> {
   m() {
     return T;
   }
 }
 
-class N<T> {
+mixin N<T> {
   n() {
     return T;
   }

tests/language/mixin/getter_regression_test.dart

@@ -2,16 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Regression test case for dart2js bug where the getter for y wasn't
 // properly mixed in.
 
 import "package:expect/expect.dart";
 
-class C {
+mixin C {
   int x = -1;
   int get y => x;
 }

tests/language/mixin/illegal_constructor_runtime_test.dart

@@ -5,11 +5,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
-class M0 {
+mixin class M0 {
   factory M0(a, b, c) => throw "uncalled";
   factory M0.named() => throw "uncalled";
 }

tests/language/mixin/illegal_constructor_test.dart

@@ -2,8 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
+// Validates mixin behavior that is only relevant pre 3.0.
 // @dart=2.19
 
 class M0 {

tests/language/mixin/illegal_cycles_test.dart

@@ -2,72 +2,74 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 class M {}
-class M0 extends Object with M0 { }
-//    ^^
+mixin class M0 extends Object with M0 { }
+//          ^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M0' is a supertype of itself.
-//    ^
+//          ^
 // [cfe] 'Object with M0' is a supertype of itself.
-//                           ^^
+//                            ^^^^^^^
 // [analyzer] COMPILE_TIME_ERROR.MIXIN_INHERITS_FROM_NOT_OBJECT
-class M1 = Object with M1;
-//    ^^
+//                                 ^^
+// [analyzer] COMPILE_TIME_ERROR.MIXIN_INHERITS_FROM_NOT_OBJECT
+mixin class M1 = Object with M1;
+//          ^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M1' is a supertype of itself.
 
-class M2 = Object with M3;
-//    ^^
+mixin class M2 = Object with M3;
+//          ^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M2' is a supertype of itself.
-class M3 = Object with M2;
-//    ^^
+mixin class M3 = Object with M2;
+//          ^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M3' is a supertype of itself.
 
-class M4 = Object with M5;
-//    ^^
+mixin class M4 = Object with M5;
+//          ^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M4' is a supertype of itself.
-class M5 = Object with M6;
-//    ^^
+mixin class M5 = Object with M6;
+//          ^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M5' is a supertype of itself.
-class M6 = Object with M4;
-//    ^^
+mixin class M6 = Object with M4;
+//          ^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M6' is a supertype of itself.
 
-class M7 extends Object with M8 { }
-//    ^^
+mixin class M7 extends Object with M8 { }
+//          ^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M7' is a supertype of itself.
-//    ^
+//          ^
 // [cfe] 'Object with M8' is a supertype of itself.
-//                           ^^
+//                            ^^^^^^^
 // [analyzer] COMPILE_TIME_ERROR.MIXIN_INHERITS_FROM_NOT_OBJECT
-class M8 extends Object with M7 { }
-//    ^^
+//                                 ^^
+// [analyzer] COMPILE_TIME_ERROR.MIXIN_INHERITS_FROM_NOT_OBJECT
+mixin class M8 extends Object with M7 { }
+//          ^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M8' is a supertype of itself.
-//    ^
+//          ^
 // [cfe] 'Object with M7' is a supertype of itself.
-//                           ^^
+//                            ^^^^^^^
+// [analyzer] COMPILE_TIME_ERROR.MIXIN_INHERITS_FROM_NOT_OBJECT
+//                                 ^^
 // [analyzer] COMPILE_TIME_ERROR.MIXIN_INHERITS_FROM_NOT_OBJECT
 
 class M9  = Object with M91;
 //    ^
 // [cfe] 'M9' is a supertype of itself.
-class M91 = Object with M92;
-//    ^^^
+mixin class M91 = Object with M92;
+//          ^^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M91' is a supertype of itself.
-class M92 = Object with M91;
-//    ^^^
+mixin class M92 = Object with M91;
+//          ^^^
 // [analyzer] COMPILE_TIME_ERROR.RECURSIVE_INTERFACE_INHERITANCE
 // [cfe] 'M92' is a supertype of itself.
 

tests/language/mixin/illegal_static_access_runtime_test.dart

@@ -5,17 +5,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 class S {
   static foo() => 42;
 }
 
-class M {
+mixin M {
   static bar() => 87;
 }
 

tests/language/mixin/illegal_static_access_test.dart

@@ -2,17 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 class S {
   static foo() => 42;
 }
 
-class M {
+mixin M {
   static bar() => 87;
 }
 

tests/language/mixin/illegal_super_use_runtime_test.dart

@@ -5,15 +5,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
-class M {}
+mixin M {}
 
-class P0 {
+mixin P0 {
   foo() {
 
 
@@ -36,7 +32,7 @@ class P0 {
   }
 }
 
-class P1 {
+mixin class P1 {
   bar() {
 
     return 87;
@@ -56,7 +52,7 @@ class P1 {
   }
 }
 
-class P2 {
+mixin class P2 {
   baz() {
 
     return 99;

tests/language/mixin/illegal_super_use_test.dart

@@ -2,15 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
-class M {}
+mixin M {}
 
-class P0 {
+mixin P0 {
   foo() {
     super.toString();
     super.foo();
@@ -51,7 +47,7 @@ class P0 {
   }
 }
 
-class P1 {
+mixin class P1 {
   bar() {
     super.toString();
     return 87;
@@ -71,7 +67,7 @@ class P1 {
   }
 }
 
-class P2 {
+mixin class P2 {
   baz() {
     super.toString();
     return 99;
@@ -80,6 +76,8 @@ class P2 {
 
 class C = Object with M;
 class D = Object with P0;
+//                    ^^
+// [analyzer] COMPILE_TIME_ERROR.MIXIN_APPLICATION_NO_CONCRETE_SUPER_INVOKED_MEMBER
 class E = Object with M, P1;
 class F = Object with P2, M;
 

tests/language/mixin/illegal_superclass_runtime_test.dart

@@ -5,19 +5,15 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 class S0 {}
 
 class S1 extends Object {}
 
 class S2 extends S0 {}
 
-class M0 {}
+mixin class M0 {}
 
-class M1 extends Object {}
+mixin class M1 extends Object {}
 
 class M2 extends M0 {}
 

tests/language/mixin/illegal_superclass_test.dart

@@ -2,21 +2,20 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 class S0 {}
 
 class S1 extends Object {}
 
 class S2 extends S0 {}
 
-class M0 {}
+mixin class M0 {}
 
-class M1 extends Object {}
+mixin class M1 extends Object {}
 
-class M2 extends M0 {}
+mixin class M2 extends M0 {}
+//                     ^^
+// [analyzer] COMPILE_TIME_ERROR.MIXIN_INHERITS_FROM_NOT_OBJECT
+// [cfe] The class 'M2' can't be used as a mixin because it extends a class other than 'Object'.
 
 class C00 = S0 with M0;
 class C01 = S0 with M1;

tests/language/mixin/illegal_syntax_test.dart

@@ -2,13 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 class S { }
 class G<T> { }
-class M { }
+mixin M { }
 
 class T0 = S with M;
 abstract class T0A = S with M;

tests/language/mixin/implements2_test.dart

@@ -2,17 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 // Regression test for named mixin applications with implements clause.
 
 class A {}
 
 class S {}
 
-class M {}
+mixin M {}
 
 class C = S with M implements A;
 

tests/language/mixin/implements_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
 abstract class I0 {
@@ -18,7 +14,7 @@ abstract class I1 {
 
 abstract class I2 implements I0, I1 {}
 
-class M {
+mixin M {
   foo() => 42;
   bar() => 87;
 }

tests/language/mixin/implicit_covariance_test.dart

@@ -2,17 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import 'package:expect/expect.dart';
 
 abstract class A<T> {
   foo(T x);
 }
 
-abstract class B<T> implements A<T> {}
+mixin B<T> implements A<T> {}
 
 class C {
   foo(num x) {

tests/language/mixin/inference_mixin_field_test.dart

@@ -2,13 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 import "package:expect/expect.dart";
 
-class Mixin {
+mixin Mixin {
   var field;
   createIt() {
     if (field == null) field = 42;

tests/language/mixin/interface_check_test.dart

@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 class Thing {}
 
 class SubThing extends Thing {
@@ -16,7 +12,7 @@ class A {
   Thing get thing => new Thing();
 }
 
-abstract class B implements A {
+mixin B implements A {
   @override
   SubThing get thing;
 }

tests/language/mixin/invalid_bound2_test.dart

@@ -2,15 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 class S0<T> {}
 
 class S<U extends num, V extends U> extends S0<String> {}
 
-class M<U extends num, V extends U> {}
+mixin M<U extends num, V extends U> {}
 
 class A<U extends num, V extends U> extends S with M {}
 

tests/language/mixin/invalid_bound_test.dart

@@ -2,15 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// TODO(51557): Decide if the mixins being applied in this test should be
-// "mixin", "mixin class" or the test should be left at 2.19.
-// @dart=2.19
-
 class S0<T> {}
 
 class S<T extends num> extends S0<String> {}
 
-class M<T extends num> {}
+mixin M<T extends num> {}
 
 class A<T extends num> extends S with M {}